The present invention is directed to an improved method of determining setback or setup in heating, ventilating and air conditioning systems (HVAC).
Setback and setup are mechanisms for saving energy during unoccupied time periods by establishing an unoccupied setpoint farther from the comfort zone than an occupied setpoint. Since the unoccupied setpoint is farther from the comfort zone, less work is required by the HVAC equipment when the unoccupied setpoint is used. Generally setback refers to lowering the heating setpoint, while setup refers to increasing the cooling setpoint. For purposes of the present invention and for brevity in explanation, setback will be used to refer to both setback and setup, and the direction of setback will depend upon whether heating or cooling is the mode of operation.
Previously, setback systems would add a fixed increment such as 4.degree. F. to the cooling setpoint to establish an unoccupied setpoint, or subtract a fixed increment such as 4.degree. F. from a heating setpoint to establish a setback temperature. Although this approach does save energy, under most conditions more energy can be saved by using more flexible strategies. Flexible strategies are particularly appropriate where an occupant is willing to tolerate greater extremes of temperature, or where the area to be cooled is a warehouse or the like which is unoccupied most of the time. In such situations, much energy can be saved by increasing the amount of setback in proportion to an areas lack of occupancy or in proportion to indications of a user's tolerance for temperature extremes.
In a setback system controlled by a time clock system, the time clock system provides a control signal whenever setback is desired and for as long as setback is desired. Typically, a control signal is provided only when setback is desired.